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Written by Aaron Balwich
Maintenance and running tips to keep your two-stroke engine happy
Technical
As seen in the August 2017 issue of Model Aviation.

Engine Speak

There is some basic engine terminology you should know to better understand and properly run your model engine. Here’s a list of common terms.

The engine case is the main body of the engine.

The head is the part on top of the engine, which is usually bolted in place with four to six bolts. In its center is a threaded hole where the glow plug is installed.

The sleeve is the inside cylinder lining that houses and guides the piston. It is a separate piece from the engine case and has openings or ports cut into its side.

Ports are channels or openings inside the engine case that transfer the fuel and air mixture from the crankcase to the combustion chamber. The ports are opened and closed by the upward and downward motion of the piston.

ABC refers to the materials used in the engine. An ABC engine is one with an aluminum (A) piston, fitted inside a brass (B) sleeve, that’s been chrome (C) plated. Most higher-quality engines have ABC construction.

The connecting rod is the part that attaches the piston to the crankshaft. The connecting rod has bushing at either end and is connected to the piston with a wrist pin and to the crankcase with a crankpin.

The Basics

Model airplanes powered by two-stroke or four-stroke glow engines have a long history in our RC hobby. Chances are, when you first started flying that you were introduced to the hobby with an electric-powered airplane. Whether it was kit-built or an ARF, all you needed to do was charge the battery pack and go. Taking a new step into RC airplanes with engines bolted into their noses is an exciting proposition. Let’s take a look at what’s involved.

Two-stroke engines are the most popular type of engines used in the hobby. They have a good power-to-weight ratio, are fairly inexpensive, and have relatively few moving parts. Maintenance is simple and with a proper break-in, a two-stroke engine will last many years.

The O.S. Max AX line of engines is excellent and they come in several sizes.

Two-stroke engines range in size from .010 cubic inch (cu. in.) displacement to 3 cu. in. and even larger. For the most part, the average engine size is .25 to .40 cu. in. displacement. For more advanced, higher-performance airplanes, .60 to .72 cu. in. two-stroke engines, and four-stroke engines in the .90 to 1.50 cu. in. range are popular.

All model airplanes have a recommended engine size range, but most perform best when you choose the upper engine size that is recommended. There’s nothing worse than an underpowered model, especially when you are trying to learn how to fly.

Engine Breakdown

The engine case is usually made up of three parts: the front housing, the crankcase itself, and the backplate. Some engines have a two-piece case design, but internally, all engines are the same.

The crankshaft is supported within the front housing with a ball bearing or bushings and has a threaded front end. A propeller nut and a propeller washer hold the propeller securely against the thrust washer at the front of the engine.

At its rear, the crankshaft has a counter weight and a crankpin that engages the bottom end of the connecting rod. The connecting rod attaches to the piston with a wrist pin. The piston fits within the engine’s sleeve, which fits into, and is supported by, the engine case. The head sits on top of the cylinder and sleeve and the space between the top of the piston and the bottom of the head is the combustion chamber.

Basic Two-Stroke Operation

A two-stroke engine completes one revolution for every power cycle. As the piston moves up it compresses a fresh charge of fuel. The fuel and air mixture heats and is combusted by the glow plug. The upward motion of the piston creates negative pressure within the crankcase below the piston and draws air and fuel from the carburetor through the intake valve.

The combustion of the fuel mixture forces the piston down in the combustion cycle, which now compresses the fresh charge of fuel. As the piston travels down and the hollow crankshaft rotates, the intake valve is closed and the intake ports are opened.

The compressed fuel charge passes through the ports and is directed into the combustion chamber. This happens just as the spent fuel charge exits the combustion chamber through the exhaust port. As the piston starts moving up again, it closes the exhaust port, opens the intake valve, and the process repeats.

Four-Stroke Engines

Four-stroke engines are also extremely popular, mostly because of their wider power band, but also because of their great sound while running. Four-stroke engines are more expensive and more complicated than two-stroke engines and require more maintenance. Instead of having intake and exhaust ports, a four-stroke engine has intake and exhaust valves, as does the engine in your family car.

A four-stroke engine, although slightly more complicated and with more internal parts, produces a great sound while running and provides excellent torque for turning larger propellers.

There’s a cam assembly driven by the crankshaft as well as lifter rods, tappets, and valve springs. Adjusted properly, four-stroke engines produce a good amount of power, but they produce their peak power at lower rpm than a two-stroke engine of the same displacement. In comparison, a .90-size four-stroke engine produces roughly the same power as a .60-size two-stroke engine.

Start-Up and Break-In

When you have a new, out-of-the-box engine, it needs special handling before you can run it at full throttle. Don’t just bolt your two-stroke engine to your airplane and go out to the flying field. Some airplane manufacturers suggest it is okay to do this, but it’s better to play it safe the first time out and break in your engine at home where you have tools and supplies handy.

To be specific, breaking in an engine is the gradual fitting together of the engine’s internal parts by making short, well-lubricated engine runs.

First, get a new glow plug and make sure it is properly installed. Next, fill the fuel tank with two-stroke fuel that has approximately 5% nitro and 18% to 20% oil. Attach the fuel line to the needle-valve assembly and make sure that the line is not kinked or resting against the engine case because it will heat up as the engine runs.

When attaching the fuel line and vent line from the fuel tank, make sure that they are not kinked or resting against the engine.

Attach the recommended size propeller and install the propeller washer and propeller nut. Snug the propeller nut down and tighten it roughly 1/4 turn. Open the needle valve at least four full turns and fully open the throttle sleeve. Place your thumb over the intake venturi and flip the propeller counterclockwise several times. You will see fuel start to move into the fuel line and flow into the carburetor.

After you have fuel to the carburetor, close the throttle sleeve to approximately 1/4 power and hook up your glow plug drive battery. For safety, I recommend either flipping the propeller over with a chicken stick or using an electric starter until the engine catches and starts to run.

Slowly open the throttle all the way and let the engine run for roughly 10 minutes with a very rich, low-power needle-valve setting. Then stop the engine and let it cool. Repeat this process several times and gradually lean out the engine by a couple of clicks of the needle valve each time.

Don’t let the engine run at high rpm (lean setting) until you have run at least four or five tanks of fuel through it. When you break in the engine, you are trying to gradually wear all of its parts so that they match one another. It is the piston and sleeve fit that we’re most concerned about.

Some engines can be broken in more quickly than others, but all of them must go through the break-in process to operate properly. If you try to run your engine without breaking it in first, it will run hot because of excess friction and localized heat caused by the metal contact points. This will eventually damage it.

You will know your engine is properly broken in when it runs consistently without overheating and it has a good transition from idle to full throttle. It is always better to operate your engine a few clicks on the rich side than a few clicks on the lean side.

The Low-End Setting

Some engines have a single needle valve and a small bleed hole, which is used for the low-end or idle-mixture setting, while others have two needles (one large one for the main and a smaller one for idle). It is during the break-in process that you will also learn how to adjust the low-end mixture setting.

The low-end needle valve is adjusted by turning the small setscrew shown in the center of the throttle arm.

Start with the setting that comes with the engine. It will usually be close to the correct setting. When you bring the engine to an idle and the engine dies, this means the setting is too lean. You must increase the amount of fuel drawn into the carburetor at idle. If the engine settles into an idle, but then burbles or dies when the throttle is opened again, the lower-end mixture setting is too rich and the amount of fuel entering the carburetor at idle must be decreased.

With a twin needle-valve design, you adjust the amount of fuel entering the carburetor with the idle needle valve. With an air-bleed design, you adjust the amount of air entering the carburetor during idle.

A typical carburetor has two needle valves to adjust the fuel/air mixture. The high-end needle assembly is shown here.

Both types of carburetors work well, but most high-powered engines rely on the twin needle-valve carburetor for mixture adjustment. It is important that your engine has a good, reliable idle before you commit your model airplane to flight.

Care and Maintenance

Proper engine care from the start will ensure that you get maximum power and longevity, so start caring for your engine the day you bring it home. Most engines come with tools such as Allen or hex wrenches to tighten and loosen the screws that hold the engine together. Keep these in a safe place and if you lose them, be sure to replace them with the correct sizes.

Glow engines need to be installed on your airplane with a strong, rugged mounting system. Your propeller should be the recommended size and properly balanced. Notice the wire extension added to the main needle valve to keep fingers clear of the propeller.

Start by removing the engine’s backplate and checking inside the crankcase for metal shavings or other foreign material. Remove the head and check the combustion chamber for the same. Squirt some 3-in-One Multi-Purpose Oil into the engine and turn the engine over. Lubricate the bearings as well as the connecting rod bushings. Check to make sure the ports in the sleeve match the ports cast or machined into the engine case.

Now reassemble the engine and tighten the screws in a crisscrossing pattern. Do not use threadlocker compound on the engine case or head screws. It is not required and will make future maintenance difficult. You could strip the threads out of the holes.

Never force anything that won’t go on or move easily. The engine is made mostly of aluminum and it is easy to damage threads. Always use the proper size wrench to tighten the propeller nut; never use vice grips or pliers. A 6-inch adjustable wrench is a good tool to keep in your field box.

After the last flight of the day, drain the fuel from the tank and run the engine dry. Squirt some after-run oil into the carburetor to coat the inside surfaces of the engine to prevent corrosion. Alcohol-based fuels attract moisture and unprotected engine surfaces will corrode—especially the ball bearings. Oil is inexpensive insurance for a long engine life.

Proper Balance

Perhaps the most important thing to do before you run your engine and install it in your airplane is to use properly balanced propellers. Good-quality propellers, for the most part, come out of the package well balanced, but to make sure your propeller is balanced, use a propeller balancer such as the one from Du-Bro Products.

Using an unbalanced propeller increases vibration. This is bad for your airplane’s structure and engine because it puts undue stress on its parts. Vibration can cause hardware to come loose and even cause control surface hinges to wear out and break during flight. Do yourself a favor and be a stickler for smooth-running, properly balanced propellers.

A Du-Bro propeller balancer is an excellent tool to add to your workshop. This precision tool allows you to fine-tune any propeller’s balance.

So, that’s it. At first it may seem as though this is a lot of effort, but it is all part of properly running and taking care of your two-stroke model airplane engine.

A good piece of advice is to find an modeler who has experience running glow engines and have him or her help you get started. The task will be easier and more fun. With proper care and feeding, you can expect your glow engine to last a lifetime.

33 comments

I’m a couple of weeks shy of eighty years old. I’ve had glow engines since I was around twelve. I’ve been flying RC since the days of transistor super regents. My first servo equipped gear was Citizenship analog proportional.

I LOVE electric stuff. It blows the doors off glow in every way. I love my old engines but strictly as works of art. The only exception is my five cylinder O.S. Radial on my Quarter Scale Fleet Bipe.

I think anyone who,WANTS to fly glow is a bit nutso. Don’t forget to bring a couple of rolls of paper towels and a full spray bottle of Fantastic and make sure you don’t drip oil on your car seats going home after a day’s flying.

Hey Pete the grouch,
let's be honest here. I have a mix of gas, glow, and electric. Here are the pro's and con's of each. Electric: Easy, if you plan to spend an hour or less at the field. I have a 36' motor home and 16' trailer to haul my toys in. Li-po's are deadly, and demand the best care and storage. My batteries are kept in a metal ammo box, and stored in the oven for extra security. Batteries are expensive and can be a hassle when you get so many, that they must be numbered! Then you need to separate them as to charged, stored, discharged, and there are several reasons for different states when you have a large "fleet." Power begins to diminish immediately, with no decrease in weight, and so, performance decreases during flight. Who has not nursed a dying battery back to the airfield against the wind? Two things going for electric? Quiet, and reliable. Clean, it is NOT!! You still have the same grass and mud to wipe away, which I find harder to clean off without the oil to keep it from sticking. 409 to get the grass off.
Nitro, is expensive, at $20 per gallon however, I still love the smells of my youth, the sound and the power of nitro! I fly my models the same way I fly full scale, and that is to fly as if you expect an engine failure! Choose your site wisely, fly smart, and you won't have to explain how you ended up in the tree. Gas, is the cheapest, though I find that I need to go bigger when replacing a nitro engine of the same displacement. Not nearly as messy as nitro though.
To sum up, they each have their place and worth. I love all of my planes, but I can fly gas and glow all day, when the hundreds of dollars in batteries, are awaiting their turn on my six port charger, in just a couple of hours...I am also in the habit of cleaning all my planes that have flown at the end of the day. They even get treated to a coat of spray wax! The wax works great when flying in the rain!

I have been in this hobby for 38 years...grew up on glow motors Wich is really what got me into the hobby.i have 18 nitro planes and 5 pumpgas planes....0..electric!!!!!!! Lot of guys from several clubs I belong to hate electric aircraft!!!not to mention those cheap cheasy foam planes!!!!electric planes are boring they take the fun pride and joy away from once was a hobby!!no...no not nutso!!!just happy rc flyers!!!

I too am a member of the Babcock Citizenship Bonner days of the early 40's model airplanes and engines. I have tried electric airplanes along with the popular DOG airplanes (ARF ARF ARF). Because of the attitude that the I'm too busy or too impatient pilots of today have the hobby is on it's way of the model "T" ford.
Old Henry was too stubborn to try a new engine that the "T" was almost his downfall. Whenever I go to the flying field and see the guys with bandages and scars I am glad that I have remained true to the NOISY relaxing comforting sounds of yesteryear. Times when I can remember what it was like to spend several days awaiting Ambroid Testors or Elmers to dry so I could finish my pride and joy to be able to join other flyers in our Kiddy club of early builders and flyers at the local ball diamond or local airport (that's right we flew on the local airport field.) Not like today where so many of the local TOY BOYS fly in the paths of modern aircraft with no respect for the safety of the real pilots,Thus prompting the FAA to make life miserable for the REAL model Builders of today.
This is the reason we have to travel 30-40 miles to a hobby shop to get balsa and supplies to BUILD a REAL model only to have the shop owner say he doesn't stock only small limited selections of building supplies. And every year more and more big name hobby local shops are closing there doors for good. I live 75 miles from Houston where there are maybe 4 or 5 shops struggling to stay afloat due to the attitude of the modern TOY BOY electric operators. I see "modelers" spend thousands of dollars on DOGS only to have someone build the DOG (ARF) for them only to have the plane crash on the maiden flight.
I personally get great joy seeing the look on a fellow club member's face when I show up with a rebuilt ARF that somebody "rekitted" at a local flyin.
My house is too full of scratch built and rebuilt model planes to build any more(I have 26 models hanging all over my house that my grand kids will someday inherit. I am glad that I was fortunate to find an airline flight attendant to marry or I would not have my hangar of planes.

I feel the same way about electric airplanes . Most of them are like flying a piece of typing paper . But I don't think this guy should go around bashing glow engines as they a ton of fun and they fly like a real airplane .... By the way I am about the same age ..

What you call a Two Stroke engine is properly called a Two Cycle engine and it completes ONE power cycle for each revolution not two revolutions as you state. This is about as basic as it gets. The Four Cycle engine completes ONE power cycle in two revolution.

A two-stroke (or two-cycle) engine is a type of internal combustion engine which completes a power cycle with two strokes (up and down movements) of the piston during only one crankshaft revolution. This is in contrast to a "four-stroke engine", which requires four strokes of the piston to complete a power cycle during two crankshaft revolutions. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust (or scavenging) functions occurring at the same time.

Hello Bob ? Biob ? ,
In reading your comments I don't think you are understanding the articles content. Your comment that the article states 2 revolutions per power cycle is incorrect it clearly states 1 revolution per power cycle meaning that each revolution contains a power cycle, also it appears that you do not understand the term strokes as it applies to engine operation ( one upward, and one downward per revolution ) whether called a stroke or cycle it means the same thing that being one complete linear movement of the piston from the top to bottom, or bottom to top of the cylinder so 2 per revolution.
I found the article to be very informative and a good general overview (not a training seminar) of glow engines.
I have been a mechanic for over 30 years, and tinkering with all things mechanical well before that, and an avid RC pilot for 10 years (mostly Glow, with some Electrics, now trying Gas) with my favorite power source being Saito 4 strokes.

The market standard seems to identify model engines as either two-stroke or four-stroke. As an introduction to the popular power system, following naming standards is a good attempt at minimizing confusion. If this article took an engineering approach then adhering to technical terms would be more appropriate. The modern model engine is a marvel with top brands that deliver examples that practically run themselves. The experience creates a deeper appreciation and good life lessons that are well worth the effort. I can see a "How to tune a model airplane engine" as a good follow-on article.

Lots of mistakes. A simplistic and misleading piece. There is much more to the Glow Engine story than the author's universal treatment of the topic, including break-in and fuels. Enthusiasts should buy a good book or two.

I have been flying glow engine powered models since my start 60 years ago. I loved the smell and the noise and now have tinnitus and partial deafness. Those 1/2 A free flight sure climbed out nice. Fortunately I never got seriously bitten by any of my planes and had good training to be wary of electric powered props. I will never have to build another alcohol burner or as the industry prefers "nitro" model because people keep giving me their old ones after they go electric. The article failed to mention the ancient joy of replacing silk or silkspan covering on a model after it got soaked through with oil or having to rebuild the front end of a model after the saturated wood no longer could be glued to. Flyers no longer have the opportunity to better know their fellow club members while soliciting a new glow plug. I am getting old but not too old to continue enjoying my hobby.

I've been modeling for 51 years now, and made the move to electrics about 10 years ago. I am now moving back to glow and diesel. Electrics are fine but they lack soul. They have become a bit boring to me. I simply love the sound, the challenges, the mechanics and even the smell of engines. That, to me, is a large part of what I find enjoyable about the hobby. Similarly I have started building again. As with electrics, ARF's are fine, but flying what I built and covered brings an extra element of joy. Good article!

I think you all are being a little hard on the author, I'm sure he knows there is much more to taking care of the engines, but for someone who has never touched one he was trying to give them the basics, I don't think he had room to go through it all in this brief message, I'm sure when their serious about nitro engines they'll buy a manual, and the motor may be a 2 stroke, but is also called a 2 cycle, I think the article will help a lot with someone who has never tried them, that's what I started with in the mid 70's back then I never heard of an electric RC airplane, I like electric for quick set up and getting on the field faster, but I still love the little glow fuel engines, just for the mechanics, especially the 4 strokes.

It is my observation that there are fewer and fewer glow engines at the field. It seems electric rules the smaller airplanes and gas rules the larger airplanes. At my home field on Sunday there were about 20 pilots and only one using (dirty, loud and annoying) 'two-stroke glow'

I grew up flying glow engines and loved them. Then I began flying electric powered planes and the small ones especially have some nice advantages. They are easy to charge and transport and you can be at the park or field and up in the air in minutes. But the batteries require careful storage charges and handling or you may burn down your home or car. Also the batteries for the large electrics are fairly expensive and take some time to charge unless you can afford to have 5 or 6 at $100 a piece. Glow seems to me to have the advantage in the 40 - 60 size airplanes. You can carry enough fuel to fly longer than 4 minutes and you can fly as quickly as you can fuel and restart your engine. And the glow fuel smells wonderful when you are downwind of a low pass. I won't give up my small electrics because they are quick, easy, and relaxing to fly. I also won't give up my glow aircraft because I can fly all day long as often as I want to fly for as long as I want to fly. Each as distinctly different advantages. If you are proficient with electric, but have never tried glow powered aircraft, it is very different and has a bit of a learning curve, but if you ask a long time model flier....help will be available just for the asking. Try both types of models....you won't be sorry.

I am in a state of disbelief that the AMA used this article AGAIN! When it was included in the
August edition of MA, I wrote to the author and the AMA about the totally inaccurate content
of the article and stated that such misinformation should not be part of any publication from
the AMA. I also questioned whether or not there was any editorial oversight regarding the
accuracy of what gets printed in MA.
Apparently there is not, as here we are again, with connecting rod connected to the crankcase,
lifter rods, and a totally incorrect description of how a 2-stroke engine functions. Shocking!

I am in a state of total disbelief that AMA chose to run this article *again*. When it was
printed in the August edition of Model Aviation, I wrote to the author *and* the AMA,
outlining the inaccuracies and total falsehoods contained therein. Such misinformation
should not be part of any publication from the AMA. I also questioned the presence of
editorial oversight regarding the content of material submitted to the AMA for publication.
Apparently there is none, since here we are again, reading about a connecting rod connected
to the crankcase, lifter rods, and a completely incoherent, totally false description as to
how a 2-stroke engine functions. Shocking.

You should have provided information on specific books on the subject, here you go. 2-Stroke Glow Engines and Power Beyond the Basics by David Gierke, All About Engines by Harry Higley, The r/c engine and r/c 4 Stroke engine by Clarence Lee. Great reading lots of technical info and tips on how to break in and clean your engine, also trouble shooting tips. Electric planes are nice, but the sound and power of glow engines are truly wonderful.

This article should have included some books to expand on the subject, here you go. 2-Stroke Glow Engines and Power Beyond the Basics by David Gierke, All About Engines by Harry Higley, the r/c engine and r/c 4-Stroke engine by Clarence Lee. Great books that have alot of tecnical info, diagrams, engine tips and trouble shooting. The sound of a 2 or 4 stroke engine is unmistakable.

I had a good laugh when I read the line "Chances are, when you first started flying that you were introduced to the hobby with an electric-powered airplane." When I started flying no one had electric. RC cars still used brushed motors and only a very few put them in a plane. The ones that did usually flew really REALLY bad! Made me realize that I am getting old :)

It is nice to see an article on the powerplant of choice for over 100 years. The modern glow engine is a reliable power source, very easy to break in and operate. In fact, most can be broken in while in flight. I fly precision aerobatic control line and a new OS LA engine breaks in in about 4 laps or less than 1 minute of operation.

Disregard the naysayers and article sharpshooters. The glow engine connects us with the great plane designers, builders and flyers of the past. They can be bought used for as little as $20.

I find myself in awe of the old grouches who are well versed in an art or hobby and just lack enough social skill to be kind as they transmit their information. I see them in virtually every hobby, be it model aircraft, woodworking, gaming, or black powder firearms. These crotchety souls can impart a great deal of knowledge, but you have to take it with a grain of salt. It may not be gospel, and the literature is often biased. It is hard to get the best evidenced based information. It is especially fun to watch these folks disagree with another, about something that is relatively trivial. Seeing as they are probably both either on the autism spectrum or have already had small cerebral infarcts, it behooves us to be kind, nod, smile and be understanding. I'm aiming to live long enough to join their ranks... :) Best wishes and Merry Christmas..

I have been flying glow an gas for avery long time. my oppinion is these new electric are ok for some ,but I think electric has ruined the hobby. there is nothing more exciting than building an flying yer home built plane.there are less an less people building an that drives up the cost of model kits an materials for building.

The one fundamental feature of a glow engine that makes it unique is the glow plug itself; it's what gives the engine its name and makes it different from gas or diesel engines. I think the article should have led with that basic function. The catalytic reaction between the platinum wire in the plug and methanol fuel keeps the element hot and ignites the fuel, keeping the engine running after it is started and the battery is disconnected.
The mechanical aspects of glow, gas and diesel engines are very similar. It's the glow plug and methanol based fuel that define a glow engine.